Jeff Carter scored the go-ahead goal at 6:09 of the third period and nailed down the seventh victory in eight games for the defending Stanley Cup champs.
Jake Muzzin scored two goals and an assist for Los Angeles. Mike Richards and Anze Kopitar each had a goal and an assist. Slava Voynov added an insurance goal at 14:51 of the third.
The Blues, who have lost five of their last seven, also used two goalies in the game. Jaroslav Halak got the start but was pulled in the third period after allowing five goals on 21 shots. Brian Elliot allowed one goal on eight shots.